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<body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">JSON-LD Syntax 1.0</h1><h2 id="subtitle">A Context-based JSON Serialization for Linking Data</h2><h2 id="unofficial-draft-16-october-2011">Unofficial Draft 16 October 2011</h2><dl><dt>Editor:</dt><dd><a href="http://manu.sporny.org/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dt>Authors:</dt><dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dd><a href="http://digitalbazaar.com/">Dave Longley</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dd><a href="http://greggkellogg.net/">Gregg Kellogg</a>, Kellogg Associates</dd>
<dd><a href="http://webbackplane.com/">Mark Birbeck</a>, <a href="http://webbackplane.com/">Backplane Ltd.</a></dd>
</dl><p>This document is also available in this non-normative format: <a href="diff-20110911.html">diff to previous version</a>.</p><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
<div id="abstract" class="introductory section"><h2>Abstract</h2>
<p>
JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] has proven to be a highly useful object serialization and
messaging format. In an attempt to harmonize the representation of Linked Data
in JSON, this specification outlines a common JSON representation format for
expressing directed graphs; mixing both Linked Data and non-Linked Data in
a single document.
</p>
</div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
<p>This document is an experimental work in progress.</p>

<!--  <p>
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</div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.2 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#design" class="tocxref"><span class="secno">2. </span>Design</a><ul class="toc"><li class="tocline"><a href="#goals-and-rationale" class="tocxref"><span class="secno">2.1 </span>Goals and Rationale</a></li><li class="tocline"><a href="#linked-data" class="tocxref"><span class="secno">2.2 </span>Linked Data</a></li><li class="tocline"><a href="#linking-data" class="tocxref"><span class="secno">2.3 </span>Linking Data</a></li><li class="tocline"><a href="#the-context" class="tocxref"><span class="secno">2.4 </span>The Context</a></li><li class="tocline"><a href="#from-json-to-json-ld" class="tocxref"><span class="secno">2.5 </span>From JSON to JSON-LD</a></li></ul></li><li class="tocline"><a href="#basic-concepts" class="tocxref"><span class="secno">3. </span>Basic Concepts</a><ul class="toc"><li class="tocline"><a href="#iris" class="tocxref"><span class="secno">3.1 </span>IRIs</a></li><li class="tocline"><a href="#identifying-the-subject" class="tocxref"><span class="secno">3.2 </span>Identifying the Subject</a></li><li class="tocline"><a href="#specifying-the-type" class="tocxref"><span class="secno">3.3 </span>Specifying the Type</a></li><li class="tocline"><a href="#strings" class="tocxref"><span class="secno">3.4 </span>Strings</a></li><li class="tocline"><a href="#string-internationalization" class="tocxref"><span class="secno">3.5 </span>String Internationalization</a></li><li class="tocline"><a href="#datatypes" class="tocxref"><span class="secno">3.6 </span>Datatypes</a></li><li class="tocline"><a href="#multiple-objects-for-a-single-property" class="tocxref"><span class="secno">3.7 </span>Multiple Objects for a Single Property</a></li><li class="tocline"><a href="#multiple-typed-literals-for-a-single-property" class="tocxref"><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</a></li><li class="tocline"><a href="#expansion" class="tocxref"><span class="secno">3.9 </span>Expansion</a></li><li class="tocline"><a href="#compaction" class="tocxref"><span class="secno">3.10 </span>Compaction</a></li><li class="tocline"><a href="#framing" class="tocxref"><span class="secno">3.11 </span>Framing</a></li></ul></li><li class="tocline"><a href="#advanced-concepts" class="tocxref"><span class="secno">4. </span>Advanced Concepts</a><ul class="toc"><li class="tocline"><a href="#external-contexts" class="tocxref"><span class="secno">4.1 </span>External Contexts</a></li><li class="tocline"><a href="#vocabulary-prefixes" class="tocxref"><span class="secno">4.2 </span>Vocabulary Prefixes</a></li><li class="tocline"><a href="#automatic-typing" class="tocxref"><span class="secno">4.3 </span>Automatic Typing</a></li><li class="tocline"><a href="#type-coercion" class="tocxref"><span class="secno">4.4 </span>Type Coercion</a></li><li class="tocline"><a href="#chaining" class="tocxref"><span class="secno">4.5 </span>Chaining</a></li><li class="tocline"><a href="#identifying-unlabeled-nodes" class="tocxref"><span class="secno">4.6 </span>Identifying Unlabeled Nodes</a></li><li class="tocline"><a href="#aliasing-keywords" class="tocxref"><span class="secno">4.7 </span>Aliasing Keywords</a></li><li class="tocline"><a href="#normalization" class="tocxref"><span class="secno">4.8 </span>Normalization</a></li></ul></li><li class="tocline"><a href="#markup-examples" class="tocxref"><span class="secno">A. </span>Markup Examples</a><ul class="toc"><li class="tocline"><a href="#rdfa" class="tocxref"><span class="secno">A.1 </span>RDFa</a></li><li class="tocline"><a href="#microformats" class="tocxref"><span class="secno">A.2 </span>Microformats</a></li><li class="tocline"><a href="#microdata" class="tocxref"><span class="secno">A.3 </span>Microdata</a></li></ul></li><li class="tocline"><a href="#mashing-up-vocabularies" class="tocxref"><span class="secno">B. </span>Mashing Up Vocabularies</a></li><li class="tocline"><a href="#iana-considerations" class="tocxref"><span class="secno">C. </span>IANA Considerations</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">D. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">E. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">E.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">E.2 </span>Informative references</a></li></ul></li></ul></div>



<div id="introduction" class="section">

<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2>

<p>
JSON, as specified in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>], is a simple language for representing
data on the Web. Linked Data is a technique for creating a graph of interlinked data across
different
documents or Web sites. Data entities are described using <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s,
which are typically dereferencable and thus may be used to find more
information about an entity, creating a &quot;Web of Knowledge&quot;. JSON-LD is intended to be a simple
publishing method for expressing not only Linked Data in JSON, but also for adding
semantics to existing JSON.
</p>

<p>
JSON-LD is designed as a light-weight syntax that can be used to express
Linked Data. It is primarily intended to be a way to use Linked Data
in Javascript and other Web-based programming environments. It is also
useful when building interoperable Web services and when storing Linked
Data in JSON-based document storage engines. It is practical and designed
to be as simple as possible, utilizing the large number of JSON parsers
and libraries available today. It is designed to be able to
express key-value pairs, RDF data, RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] data, Microformats
[<cite><a class="bibref" rel="biblioentry" href="#bib-MICROFORMATS">MICROFORMATS</a></cite>] data, and Microdata [<cite><a class="bibref" rel="biblioentry" href="#bib-MICRODATA">MICRODATA</a></cite>]. That is, it supports
every major Web-based structured data model in use today.
</p>

<p>
The syntax does not necessarily require applications to change their JSON, but
allows to easily add meaning by adding context in a way that is either in-band or
out-of-band. The syntax is designed to not disturb already deployed systems
running on JSON, but provide a smooth upgrade path from JSON to JSON with
added semantics. Finally, the format is intended to be easy to parse, efficient to
generate, convertible to RDF in one pass, and require a very small memory footprint
in order to operate.
</p>

<div id="how-to-read-this-document" class="section">
<h3><span class="secno">1.1 </span>How to Read this Document</h3>

<p>
This document is a detailed specification for a serialization of Linked
Data in JSON. The document is primarily intended for the following audiences:
</p>

<ul>
  <li>Web developers that want to understand the design decisions and
  language syntax for JSON-LD.</li>
  <li>Software developers that want to encode Microformats, RDFa, or Microdata
  in a way that is cross-language compatible via JSON.</li>
  <li>Software developers that want to implement processors and APIs for
  JSON-LD.</li>
</ul>

<p>
To understand the basics in this specification you must first be familiar with
JSON, which is detailed in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>]. To understand the API and how it is
intended to operate  in a programming environment, it is useful to have working
knowledge of the JavaScript programming language [<cite><a class="bibref" rel="biblioentry" href="#bib-ECMA-262">ECMA-262</a></cite>] and
WebIDL [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]. To understand how JSON-LD maps to RDF, it is helpful to be
familiar with the basic RDF concepts [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>].</p>

<p>
  Examples may contain references to existing vocabularies and use <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>es to refer to Web Vocabularies. The following is a list of all vocabularies and their <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a> abbreviations, as used in this document:
</p>
<ul>
  <li>The <a href="http://purl.org/dc/terms/">Dublin Core</a>
  vocabulary (abbreviation: <code>dc</code>, e.g., <code>dc:title</code>)</li>
  <li>The <a href="http://xmlns.com/foaf/0.1/">Friend of a Friend</a>
  vocabulary (abbreviation: <code>foaf</code>, e.g., <code>foaf:knows</code>)</li>
  <li>The <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#">RDF</a>
  vocabulary (abbreviation: <code>rdf</code>, e.g., <code>rdf:type</code>)</li>
  <li>The <a href="http://www.w3.org/2001/XMLSchema#">XSD</a>
  vocabulary (abbreviation: <code>xsd</code>, e.g., <code>xsd:integer</code>)</li>
</ul>

<p>
  JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] defines several terms which are used throughout this document:
  </p><dl>
    <dt><dfn title="JSON_Object" id="dfn-json_object">JSON Object</dfn></dt><dd>
      An object structure is represented as a pair of curly brackets surrounding zero or
      more name/value pairs (or members). A name is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>. A single colon comes after
      each name, separating the name from the value. A single comma separates a value
      from a following name. The names within an object <em class="rfc2119" title="should">should</em> be unique.
    </dd>
    <dt><dfn title="array" id="dfn-array">array</dfn></dt>
    <dd>
      An array is an ordered collection of values. An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas.  Within JSON-LD, array order is not preserved by default, unless
      specific markup is provided (see <a href="#lists">Lists</a>). This is because the basic data model of JSON-LD
      is a directed <a class="tref" title="graph">graph</a>, which is inherently unordered.
    </dd>
    <dt><dfn title="string" id="dfn-string">string</dfn></dt><dd>
      A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A
      character is represented as a single character string.
    </dd>
    <dt><dfn title="number" id="dfn-number">number</dfn></dt>
    <dd>
      A number is is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.</dd>
    <dt><dfn title="true" id="dfn-true">true</dfn> and <dfn title="false" id="dfn-false">false</dfn></dt><dd>
      Boolean values.
    </dd>
    <dt><dfn title="null" id="dfn-null">null</dfn></dt><dd>
      The use of the <em>null</em> value is undefined within JSON-LD.
      <div class="issue">Supporting <em>null</em> in JSON-LD might have a number of advantages and should be evaluated. This is currently an <a href="https://github.com/json-ld/json-ld.org/issues/11">open issue</a>.</div>
    </dd>
  </dl>
<p></p>
</div>

<div id="contributing" class="section">
<h3><span class="secno">1.2 </span>Contributing</h3>

<p>There are a number of ways that one may participate in the development of
this specification:</p>

<ul>
<li>Technical discussion typically occurs on the public mailing list:
<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
</li>

<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
on Tuesdays at 1500UTC on the second and fourth week of each month.
</li>

<li>Specification bugs and issues should be reported in the
<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>

<li><a href="https://github.com/json-ld/json-ld.org/tree/main/spec">Source code</a> for the
specification can be found on Github.</li>

<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
IRC channel is available for real-time discussion on irc.freenode.net.</li>
</ul>

</div>

</div>

<div id="design" class="section">

<!-- OddPage -->
<h2><span class="secno">2. </span>Design</h2>

<p>The following section outlines the design goals and rationale behind the
JSON-LD markup language.
</p>

<div id="goals-and-rationale" class="section">
<h3><span class="secno">2.1 </span>Goals and Rationale</h3>

<p>
A number of design considerations were explored during the creation of this
markup language:
</p>

<dl>
 <dt>Simplicity</dt>
 <dd>Developers need only know JSON and three keywords to use the basic
 functionality in JSON-LD. No extra processors or software libraries are
 necessary to use JSON-LD in its most basic form. The language attempts to
 ensure that developers have an easy learning curve.</dd>
 <dt>Compatibility</dt>
 <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
 all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
 <dt>Expressiveness</dt>
 <dd>The syntax must be able to express directed graphs, which have been proven
 to be able to simply express almost every real world data model.</dd>
 <dt>Terseness</dt>
 <dd>The JSON-LD syntax must be very terse and human readable, requiring as
 little as possible effort from the developer.</dd>
 
<!-- <dt>Pragmatism</dt>
 <dd>Mixing the expression of pure Linked Data with data that is not
 linked was an approach that was driven by pragmatism. JSON-LD attempts to be
 more practical than theoretical in its approach to Linked Data.</dd> -->

 <dt>Zero Edits, most of the time</dt>
 <dd>JSON-LD provides a mechanism that allows developers to specify
 context in a way that is out-of-band. This allows organizations that have
 already deployed large JSON-based infrastructure to add meaning to their
 JSON documents in a way that is not disruptive to their day-to-day operations and is
 transparent to their current customers. At times, mapping JSON to
 a graph representation can become difficult. In these instances, rather than
 having JSON-LD support esoteric markup, we chose not to support the use case
 and support a simplified syntax instead. So, while Zero Edits is a goal,
 it is not always possible without adding great complexity to the language.
 </dd>
 <dt>One-pass Processing</dt>
 <dd>JSON-LD supports one-pass processing, which results in a very small memory 
 footprint when processing documents. For example, to convert a JSON-LD document
 into an RDF document of any kind, only one pass is required over the data.</dd>
</dl>
</div>

<div id="linked-data" class="section">
<h3><span class="secno">2.2 </span>Linked Data</h3>
<p>
The following definition for <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> is the one that will
be used for this specification.
</p>
<ol>
  <li><dfn title="Linked_Data" id="dfn-linked_data">Linked Data</dfn> is a set of documents, each containing a representation of a linked data graph.</li>
  <li>A <dfn title="linked_data_graph" id="dfn-linked_data_graph">linked data graph</dfn> is an unordered labeled directed graph, where nodes are <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s or <a class="tref internalDFN" title="object" href="#dfn-object">object</a>s, and edges are properties.</li>
  <li>A <dfn title="subject" id="dfn-subject">subject</dfn> is any node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one outgoing edge.</li>
  <li>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a> (an Internationalized Resource Identifier as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>]).</li>
  <li>An <dfn title="object" id="dfn-object">object</dfn> is a node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one incoming edge.</li>
  <li>An <a class="tref internalDFN" title="object" href="#dfn-object">object</a> <em class="rfc2119" title="may">may</em> be labeled with an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>.</li>
  <li>An object <em class="rfc2119" title="may">may</em> be a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a> at the same time.</li>
  <li>A <dfn title="property" id="dfn-property">property</dfn> is an edge of the <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>.</li>
  <li>A <a class="tref internalDFN" title="property" href="#dfn-property">property</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>.</li>
  <li>An <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a> that is a label in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> <em class="rfc2119" title="should">should</em> be dereferencable to a <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> document describing the labeled <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, <a class="tref internalDFN" title="object" href="#dfn-object">object</a> or <a class="tref internalDFN" title="property" href="#dfn-property">property</a>.</li>
  <li>A <dfn title="literal" id="dfn-literal">literal</dfn> is an <a class="tref internalDFN" title="object" href="#dfn-object">object</a> with a label that is not an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a></li>
</ol>

<p>
Note that the definition for <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a> above is silent on the
topic of unlabeled nodes. Unlabeled nodes are not considered
<a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a>. However, this specification allows for the expression
of unlabled nodes, as most graph-based data sets on the Web contain a number
of associated nodes that are not named and thus are not directly
de-referenceable.
</p>
</div>

<div id="linking-data" class="section">
<h3><span class="secno">2.3 </span>Linking Data</h3>

<p>
An Internationalized Resource Identifier
(<dfn title="IRI" id="dfn-iri"><abbr title="Internationalized Resource Identifier">IRI</abbr></dfn>),
as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>], is a mechanism for representing unique
identifiers on the web. In <a class="tref internalDFN" title="Linked_Data" href="#dfn-linked_data">Linked Data</a>, an IRI is commonly
used for expressing a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, a <a class="tref internalDFN" title="property" href="#dfn-property">property</a> or an
<a class="tref internalDFN" title="object" href="#dfn-object">object</a>.
</p>

<p>JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean
that JSON-LD requires every key or value to be an IRI, but rather ensures that
keys and values can be mapped to IRIs if the developer desires to transform
their data into Linked Data. There are a few techniques that can ensure
that developers will generate good Linked Data for the Web. JSON-LD
formalizes those techniques.
</p>

<p>We will be using the following JSON markup as the example for the
rest of this section:
</p>

<pre class="example">{
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>
</div>

<div id="the-context" class="section">
<h3><span class="secno">2.4 </span>The Context</h3>

<p>In JSON-LD, a context is used to map <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s, i.e., keys and values
  in an JSON document, to
  <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s. A <dfn title="term" id="dfn-term">term</dfn> is a short word that <em class="rfc2119" title="may">may</em> be expanded
to an <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>. The Web uses IRIs for unambiguous identification. The
idea is that these <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s mean something that may be of use to
other developers and that it is useful to give them an unambiguous identifier.
That is, it is useful for <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s to expand to IRIs so that
developers don't accidentally step on each other's Web Vocabulary terms.
For example, the term <code>name</code> may map directly to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to
be constructed using the common JSON practice of simple name/value pairs while
ensuring that the data is useful outside of the page, API or database in which it
resides.
</p>

<p>These Linked Data <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s are typically collected in a context document that would look something like this:</p>

<pre class="example">{
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
    &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
}</pre>

<p>This context document can then be used in an JSON-LD document by adding a 
single line. The JSON markup as shown in the previous section could be changed 
as follows to link to the context document:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;,</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>The additions above transform the previous JSON document into a JSON document
with added semantics because the <code>@context</code> specifies how the
<strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong>
terms map to IRIs.
Mapping those keys to IRIs gives the data global context. If two
developers use the same IRI to describe a property, they are more than likely
expressing the same concept. This allows both developers to re-use each others
data without having to agree to how their data will inter-operate on a
site-by-site basis. Contexts may also contain datatype information
for certain <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s as well as other processing instructions for
the JSON-LD processor.</p>
<p>Contexts may be specified in-line. This ensures that JSON-LD documents
can be processed when a JSON-LD processor does not have access to the Web.</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: {
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
    &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
  },</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>JSON-LD strives to ensure that developers don't have to change the JSON
  that is going into and being returned from their Web APIs. This means
  that developers can also specify a context for JSON data in an out-of-band
  fashion. This is described later in this document. </p>

<p>
  JSON-LD uses a special type of machine-readable document called a
  <dfn title="Web_Vocabulary" id="dfn-web_vocabulary">Web Vocabulary</dfn> to define <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s that are then used
  to describe concepts and &quot;things&quot; in the world.
  Typically, these Web Vocabulary documents have <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>es associated
  with them and contain a number of <a class="tref internalDFN" title="term" href="#dfn-term">term</a> declarations. A
  <dfn title="prefix" id="dfn-prefix">prefix</dfn>, like a <a class="tref internalDFN" title="term" href="#dfn-term">term</a>, is a short word that expands
  to a Web Vocabulary base IRI. <a class="tref internalDFN" title="Prefix" href="#dfn-prefix-1">Prefix</a>es are helpful when a developer
  wants to mix multiple vocabularies together in a context, but does not want
  to go to the trouble of defining every single term in every single vocabulary.
  Some Web Vocabularies may have dozens of terms defined. If a developer wants to use
  3-4 different vocabularies, the number of terms that
  would have to be declared in a single context could become quite large. To
  reduce the number of different terms that must be defined, JSON-LD also allows
  prefixes to be used to compact IRIs.
</p><p>

</p><p>For example, the IRI <code>http://xmlns.com/foaf/0.1/</code>
specifies a <a class="tref internalDFN" title="Web_Vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> which may be represented using the
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>. The <code>foaf</code> Web Vocabulary
contains a term called <strong>name</strong>. If you join the
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a> with the <strong>name</strong> suffix,
you can build a compact IRI that will expand out into an absolute IRI for the
<code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
That is, the compact IRI, or short-form, is <code>foaf:name</code> and the
expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary
term is used to specify a person's name.
</p>

<p>Developers, and machines, are able to use this IRI (plugging it
directly into a web browser, for instance) to go to the term and get a
definition of what the term means. Much like we can use <a href="http://wordnet.princeton.edu/">WordNet</a> today to
see the definition
of words in the English language. Developers and machines need the same sort of
definition of terms. IRIs provide a way to ensure that these terms
are unambiguous.
</p>

<p>The context provides a collection of vocabulary <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s and
<a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>es that can be used to expand JSON keys and values into
<a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s.</p>

<p class="note">To ensure the best possible performance, it is a best practice to
put the context definition at the top of the JSON-LD document. If it isn't listed
first, processors have to save each key-value pair until the context is processed.
This creates a memory and complexity burden for one-pass processors.</p>

</div>

<div id="from-json-to-json-ld" class="section">
<h3><span class="secno">2.5 </span>From JSON to JSON-LD</h3>

<p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>,
and <strong>avatar</strong>,
are defined in a context, and that context is used to resolve the
names in JSON objects, machines are able to automatically expand the terms to
something meaningful and unambiguous, like this:</p>

<pre class="example">{
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/homepage</span>&quot;: &quot;http://manu.sporny.org&quot;
  &quot;<span class="diff">http://rdfs.org/sioc/ns#avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Doing this allows JSON to be unambiguously machine-readable without
requiring developers to drastically change their workflow.</p>
<p class="note">Please note that this JSON-LD document doesn't define the
subject and will thus result in an unlabeled or blank node.</p>

</div>

</div>



<div id="basic-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">3. </span>Basic Concepts</h2>

<p>JSON-LD is designed to ensure that Linked Data concepts can be marked
up in a way that is simple to understand and author by Web developers. In many
cases, regular JSON markup can become Linked Data with the simple addition
of a context. As more JSON-LD features are used, more semantics are added
to the JSON markup.</p>

<div id="iris" class="section">
<h3><span class="secno">3.1 </span>IRIs</h3>

<p>Expressing IRIs are fundamental to Linked Data as that is how most
<a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s and many <a class="tref internalDFN" title="object" href="#dfn-object">object</a> are named. IRIs can be
expressed in a variety of different ways in JSON-LD.</p>

<ol>
  <li>In general, <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s in the key position in
    a <a class="tref internalDFN" title="JSON_object" href="#dfn-json_object">JSON object</a> that have a mapping to an IRI or another key in the context are
    expanded to an IRI by JSON-LD processors. There are special rules for
    processing keys in <code>@context</code> and when dealing with keys that
    start with the <code>@subject</code> character.</li>
  <li>An IRI is generated for the value specified using <code>@subject</code>,
    if it is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>.</li>
  <li>An IRI is generated for the value specified using <code>@type</code>.</li>
  <li>An IRI is generated for the value specified using the <code>@iri</code>
    keyword.</li>
  <li>An IRI is generated when there are <code>@coerce</code> rules in
    effect for a key named <code>@iri</code>.</li>
</ol>

<p>IRIs can be expressed directly in the key position like so:
</p>

<pre class="example">{
...
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p>In the example above, the key
<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an IRI, as
opposed to being interpreted as a string.</p>

<p>Term expansion occurs for IRIs if a term is defined within the
<a class="tref" title="active_context">active context</a>:</p>

<pre class="example">{
  &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;},
...
  &quot;<span class="diff">name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p><a class="tref internalDFN" title="Prefix" href="#dfn-prefix-1">Prefix</a>es are expanded when used in keys:</p>

<pre class="example">{
  &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">foaf</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/</span>&quot;},
...
  &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p><code>foaf:name</code> above will automatically expand out to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>.</p>

<p>An IRI is generated when a value is associated with a key using
the <code>@iri</code> keyword:</p>

<pre class="example">{
...
  &quot;homepage&quot;: { &quot;<span class="diff">@iri</span>&quot;: &quot;http://manu.sporny.org&quot; }
...
}</pre>

<p>If type coercion rules are specified in the <code>@context</code> for
a particular vocabulary term, an IRI is generated:</p>

<pre class="example">{<span class="diff">
  &quot;@context&quot;:
  {
    ...
    &quot;@coerce&quot;:
    {
      &quot;@iri&quot;: &quot;homepage&quot;
    }
  }</span>
...
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
...
}</pre>

<p>Even though the value <code>http://manu.sporny.org/</code> is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>,
the type coercion rules will transform the value into an IRI when processed
by a JSON-LD Processor</p>

</div>

<div id="identifying-the-subject" class="section">
<h3><span class="secno">3.2 </span>Identifying the Subject</h3>

<p>
  To be able to externally reference nodes, it is important that each node has an unambiguous identifier.
  <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>s are a fundamental concept of Linked Data, and nodes should have a de-referencable
  identifier used to name and locate them. For nodes to be truely linked, de-referencing the identifier
  should result in a representation of that node. Associating an IRI with a node tells an application
  that the returned document contains a description of the node requested.
</p>
<p>
  JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to
  uniquely identify each node which may be externally referenced.
</p>
<p>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>
   of an object in JSON is declared using the <code>@subject</code> key. The subject is the
first piece of information needed by the JSON-LD processor in order to
create the (subject, property, object) tuple, also known as a triple.</p>

<pre class="example">{
...
  &quot;<span class="diff">@subject</span>&quot;: &quot;<span class="diff">http://example.org/people#joebob</span>&quot;,
...
}</pre>

<p>The example above would set the subject to the IRI
<code>http://example.org/people#joebob</code>.
</p>

<p class="note">To ensure the best possible performance, it is a best practice to
put the <code>@subject</code> key before other key-value pairs in an object. If
it isn't listed first, processors have to save each key-value pair until
<code>@subject</code> is processed before they can create valid triples. This
creates a memory and complexity burden for one-pass processors.</p>

</div>

<div id="specifying-the-type" class="section">
<h3><span class="secno">3.3 </span>Specifying the Type</h3>

<p>The type of a particular subject can be specified using the
<code>@type</code> key. Specifying the type in this way will generate a
triple of the form (subject, type, type-iri).</p>

<p>To be Linked Data, types <em class="rfc2119" title="must">must</em> be uniquely identified by an
  <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>.</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/Person</span>&quot;,
...
}</pre>

<p>The example above would generate the following triple if the JSON-LD
document is mapped to RDF (in N-Triples notation):</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

</div>

<div id="strings" class="section">
<h3><span class="secno">3.4 </span>Strings</h3>

<p>Regular text strings, also referred to as <dfn title="plain_literal" id="dfn-plain_literal">plain literal</dfn>s, are
easily expressed using regular JSON <a class="tref internalDFN" title="string" href="#dfn-string">string</a>s.</p>

<pre class="example">{
...
  &quot;name&quot;: &quot;<span class="diff">Mark Birbeck</span>&quot;,
...
}</pre>

</div>

<div id="string-internationalization" class="section">
<h3><span class="secno">3.5 </span>String Internationalization</h3>

<p>JSON-LD makes an assumption that strings with associated language encoding
information are not very common when used in JavaScript and Web Services.
Thus, it takes a little more effort to express strings with associated
language information.</p>

<pre class="example">{
...
  &quot;name&quot;: <span class="diff">
  {
    &quot;@literal&quot;: &quot;花澄&quot;,
    &quot;@language&quot;: &quot;ja&quot;
  }</span>
...
}</pre>

<p>The example above would generate a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a> for
<em>花澄</em> and associate the <code>ja</code> language code with the triple
that is generated. Languages <em class="rfc2119" title="must">must</em> be expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>] format.</p>

</div>

<div id="datatypes" class="section">
<h3><span class="secno">3.6 </span>Datatypes</h3>

<p>
  A value with an associated datatype, also known as a
  <dfn title="typed_literal" id="dfn-typed_literal">typed literal</dfn>, is indicated by associating a literal with
  an IRI which indicates the literal's datatype. Typed literals may be
  expressed in JSON-LD in three ways:
</p>

<ol>
  <li>By utilizing the <code>@coerce</code> keyword.</li>
  <li>By utilizing the expanded form for specifying objects.</li>
  <li>By using a native JSON datatype.</li>
</ol>

<p>The first example uses the <code>@coerce</code> keyword to express a
typed literal:</p>

<pre class="example">{<span class="diff">
  &quot;@context&quot;:
  {
    &quot;modified&quot;:  &quot;http://purl.org/dc/terms/modified&quot;,
    &quot;dateTime&quot;: &quot;http://www.w3.org/2001/XMLSchema#dateTime&quot;
    &quot;@coerce&quot;:
    {
      &quot;dateTime&quot;: &quot;modified&quot;
    }
  }</span>
...
  &quot;modified&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
...
}</pre>

<p>The second example uses the expanded form for specifying objects:</p>

<pre class="example">{
...
  &quot;modified&quot;: <span class="diff">
  {
    &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
    &quot;@datatype&quot;: &quot;dateTime&quot;
  }</span>
...
}</pre>

<p>Both examples above would generate an object with the literal value of
<code>2010-05-29T14:17:39+02:00</code> and the datatype of
<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>

<p>The third example uses a built-in native JSON type, a
  <a class="tref internalDFN" title="number" href="#dfn-number">number</a>, to express a datatype:</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;age&quot;: <span class="diff">31</span>
...
}</pre>

<p>The example above would generate the following triple:</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      &quot;31&quot;^^&lt;http://www.w3.org/2001/XMLSchema#integer&gt; .</pre>

</div>

<div id="multiple-objects-for-a-single-property" class="section">
<h3><span class="secno">3.7 </span>Multiple Objects for a Single Property</h3>

<p>A JSON-LD author can express multiple triples in a compact way by using
<a class="tref internalDFN" title="array" href="#dfn-array">array</a>s. If a subject has multiple values for the same property, the author
<em class="rfc2119" title="may">may</em> express each property as an <a class="tref internalDFN" title="array" href="#dfn-array">array</a>.</p>

<p class="note">In JSON-LD, multiple objects on a property are not ordered. This is because typically graphs
are not inherently ordered data structures. To see more on creating ordered collections
in JSON-LD, see <a href="#lists">Lists</a>.
</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;joe&quot; .
&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;bob&quot; .
&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;jaybee&quot; .</pre>

</div>

<div id="multiple-typed-literals-for-a-single-property" class="section">
<h3><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</h3>

<p>Multiple <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s may also be expressed using the expanded
form for objects:</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/articles/8&quot;,
  &quot;modified&quot;: <span class="diff">
  [
    {
      &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
      &quot;@datatype&quot;: &quot;dateTime&quot;
    },
    {
      &quot;@literal&quot;: &quot;2010-05-30T09:21:28-04:00&quot;,
      &quot;@datatype&quot;: &quot;dateTime&quot;
    }
  ]</span>
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">&lt;http://example.org/articles/8&gt;
   &lt;http://purl.org/dc/terms/modified&gt;
      &quot;2010-05-29T14:17:39+02:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .
&lt;http://example.org/articles/8&gt;
   &lt;http://purl.org/dc/terms/modified&gt;
      &quot;2010-05-30T09:21:28-04:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .</pre>

</div>

<div id="expansion" class="section">
<h3><span class="secno">3.9 </span>Expansion</h3>

<p>Expansion is the process of taking a JSON-LD document and applying a
context such that all IRI, datatypes, and literal values are expanded so
that the context is no longer necessary. JSON-LD document expansion
is typically used as a part of <a href="#normalization">Framing</a> or
<a href="#normalization">Normalization</a>.</p>

<p>For example, assume the following JSON-LD input document:</p>

<pre class="example">{
   &quot;@context&quot;:
   {
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;@coerce&quot;:
      {
         &quot;@iri&quot;: &quot;homepage&quot;
      }
   },
   &quot;name&quot;: &quot;Manu Sporny&quot;,
   &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;
}</pre>

<p>Running the JSON-LD Expansion algorithm against the JSON-LD input document
provided above would result in the following output:</p>

<pre class="example">{
   &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
   &quot;http://xmlns.com/foaf/0.1/homepage&quot;:
   {
      &quot;@iri&quot;: &quot;http://manu.sporny.org/&quot;
   }
}</pre>

</div>

<div id="compaction" class="section">
<h3><span class="secno">3.10 </span>Compaction</h3>

<p>Compaction is the process of taking a JSON-LD document and applying a
context such that the most compact form of the document is generated. JSON
is typically expressed in a very compact, key-value format. That is, full
IRIs are rarely used as keys. At times, a JSON-LD document may be received
that is not in its most compact form. JSON-LD, via the API, provides a way
to compact a JSON-LD document.
</p>

<p>For example, assume the following JSON-LD input document:</p>

<pre class="example">{
   &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
   &quot;http://xmlns.com/foaf/0.1/homepage&quot;:
   {
      &quot;@iri&quot;: &quot;http://manu.sporny.org/&quot;
   }
}</pre>

<p>Additionally, assume the following developer-supplied JSON-LD context:</p>

<pre class="example">{
   &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
   &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
   &quot;@coerce&quot;:
   {
      &quot;@iri&quot;: &quot;homepage&quot;
   }
}</pre>

<p>Running the JSON-LD Compaction algorithm given the context supplied above
against the JSON-LD input document provided above would result in the following
output:</p>

<pre class="example">{
   &quot;@context&quot;:
   {
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;@coerce&quot;:
      {
         &quot;@iri&quot;: &quot;homepage&quot;
      }
   },
   &quot;name&quot;: &quot;Manu Sporny&quot;,
   &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;
}</pre>

<p>The compaction algorithm also enables the developer to map any expanded
format into an application-specific compacted format. While the context
provided above mapped <code>http://xmlns.com/foaf/0.1/name</code> to
<strong>name</strong>, it could have also mapped it to any arbitrary string
provided by the developer.
</p>

</div>

<div id="framing" class="section">
<h3><span class="secno">3.11 </span>Framing</h3>

<p>A JSON-LD document is a representation of a directed graph. A single
directed graph can have many different serializations, each expressing
exactly the same information. Developers typically work with trees, represented as
<a class="tref internalDFN" title="JSON_object" href="#dfn-json_object">JSON object</a>s. While mapping a graph to
a tree can be done, the layout of the end result must be specified in advance.
A <dfn title="Frame" id="dfn-frame">Frame</dfn> can be used by a developer on a JSON-LD document to
specify a deterministic layout for a graph.
</p>

<p>Framing is the process of taking a JSON-LD document, which expresses a
graph of information, and applying a specific graph layout
(called a <a class="tref internalDFN" title="Frame" href="#dfn-frame">Frame</a>).
</p>

<p>The JSON-LD document below expresses a library, a book and a chapter:</p>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;Book&quot;:         &quot;http://example.org/vocab#Book&quot;,
    &quot;Chapter&quot;:      &quot;http://example.org/vocab#Chapter&quot;,
    &quot;contains&quot;:     &quot;http://example.org/vocab#contains&quot;,
    &quot;creator&quot;:      &quot;http://purl.org/dc/terms/creator&quot;
    &quot;description&quot;:  &quot;http://purl.org/dc/terms/description&quot;
    &quot;Library&quot;:      &quot;http://example.org/vocab#Library&quot;,
    &quot;title&quot;:        &quot;http://purl.org/dc/terms/title&quot;,
    &quot;@coerce&quot;:
    {
      &quot;@iri&quot;: &quot;contains&quot;
    },
  },
  &quot;@subject&quot;:
  [{
    &quot;@subject&quot;: &quot;http://example.com/library&quot;,
    &quot;@type&quot;: &quot;Library&quot;,
    &quot;contains&quot;: &quot;http://example.org/library/the-republic&quot;
  },
  {
    &quot;@subject&quot;: &quot;http://example.org/library/the-republic&quot;,
    &quot;@type&quot;: &quot;Book&quot;,
    &quot;creator&quot;: &quot;Plato&quot;,
    &quot;title&quot;: &quot;The Republic&quot;,
    &quot;contains&quot;: &quot;http://example.org/library/the-republic#introduction&quot;
  },
  {
    &quot;@subject&quot;: &quot;http://example.org/library/the-republic#introduction&quot;,
    &quot;@type&quot;: &quot;Chapter&quot;,
    &quot;description&quot;: &quot;An introductory chapter on The Republic.&quot;,
    &quot;title&quot;: &quot;The Introduction&quot;
  }]
}</pre>

<p>Developers typically like to operate on items in a hierarchical, tree-based
fashion. Ideally, a developer would want the data above sorted into top-level
libraries, then the books that are contained in each library, and then the
chapters contained in each book. To achieve that layout, the developer can
define the following <a class="tref internalDFN" title="frame" href="#dfn-frame">frame</a>:</p>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;Book&quot;:         &quot;http://example.org/vocab#Book&quot;,
    &quot;Chapter&quot;:      &quot;http://example.org/vocab#Chapter&quot;,
    &quot;contains&quot;:     &quot;http://example.org/vocab#contains&quot;,
    &quot;creator&quot;:      &quot;http://purl.org/dc/terms/creator&quot;
    &quot;description&quot;:  &quot;http://purl.org/dc/terms/description&quot;
    &quot;Library&quot;:      &quot;http://example.org/vocab#Library&quot;,
    &quot;title&quot;:        &quot;http://purl.org/dc/terms/title&quot;
  },
  &quot;@type&quot;: &quot;Library&quot;,
  &quot;contains&quot;: {
    &quot;@type&quot;: &quot;Book&quot;,
    &quot;contains&quot;: {
      &quot;@type&quot;: &quot;Chapter&quot;
    }
  }
}</pre>

<p>When the framing algorithm is run against the previously defined
JSON-LD document, paired with the <a class="tref internalDFN" title="frame" href="#dfn-frame">frame</a> above, the following
JSON-LD document is the end result:</p>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;Book&quot;:         &quot;http://example.org/vocab#Book&quot;,
    &quot;Chapter&quot;:      &quot;http://example.org/vocab#Chapter&quot;,
    &quot;contains&quot;:     &quot;http://example.org/vocab#contains&quot;,
    &quot;creator&quot;:      &quot;http://purl.org/dc/terms/creator&quot;
    &quot;description&quot;:  &quot;http://purl.org/dc/terms/description&quot;
    &quot;Library&quot;:      &quot;http://example.org/vocab#Library&quot;,
    &quot;title&quot;:        &quot;http://purl.org/dc/terms/title&quot;
  },
  &quot;@subject&quot;: &quot;http://example.org/library&quot;,
  &quot;@type&quot;: &quot;Library&quot;,
  &quot;contains&quot;: {
    <span class="diff">&quot;@subject&quot;: &quot;http://example.org/library/the-republic&quot;,</span>
    &quot;@type&quot;: &quot;Book&quot;,
    <span class="diff">&quot;creator&quot;: &quot;Plato&quot;,</span>
    <span class="diff">&quot;title&quot;: &quot;The Republic&quot;,</span>
    &quot;contains&quot;: {
      <span class="diff">&quot;@subject&quot;: &quot;http://example.org/library/the-republic#introduction&quot;,</span>
      &quot;@type&quot;: &quot;Chapter&quot;,
      <span class="diff">&quot;description&quot;: &quot;An introductory chapter on The Republic.&quot;,</span>
      <span class="diff">&quot;title&quot;: &quot;The Introduction&quot;</span>
    },
  },
}</pre>

<p>The JSON-LD framing algorithm allows developers to query by example and
force a specific tree layout to a JSON-LD document.
</p>

</div>

</div>

<div id="advanced-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">4. </span>Advanced Concepts</h2>

<p>JSON-LD has a number of features that provide functionality above and beyond
the core functionality described above. The following sections outline the
features that are specific to JSON-LD.
</p>

<div id="external-contexts" class="section">
  <h3><span class="secno">4.1 </span>External Contexts</h3>

  <p>Authors may choose to declare JSON-LD <a class="tref" title="context">context</a>s in external 
documents to promote re-use of contexts as well as reduce the size of JSON-LD 
documents.
In order to use an external context, an author <em class="rfc2119" title="may">may</em> specify an IRI to a valid
JSON-LD document. If an IRI is specified, the external document <em class="rfc2119" title="must">must</em> be 
dereferenced and the top-level <code>@context</code> key in the 
<a class="tref internalDFN" title="JSON_Object" href="#dfn-json_object">JSON Object</a> <em class="rfc2119" title="must">must</em> be overlayed on top of the current 
active context.</p>

  <p>The following example demonstrates the use of an external context:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;</span>,
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Authors may also import multiple contexts by specifying a list of 
contexts to import:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: [&quot;http://example.org/json-ld-contexts/person&quot;, &quot;http://example.org/json-ld-contexts/event&quot;]</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  <span class="diff">&quot;celebrates&quot;:
  {
     &quot;@type&quot;: &quot;Event&quot;,
     &quot;description&quot;: &quot;International Talk Like a Pirate Day&quot;,
     &quot;date&quot;: &quot;R/2011-09-19&quot;
  }</span>
}</pre>

<p>Each context in a list will be evaluated in-order. Duplicate values <em class="rfc2119" title="must">must</em> be
overwritten on a last-defined-overrides basis. The context list <em class="rfc2119" title="must">must</em> contain
either de-referenceable IRIs or <a class="tref internalDFN" title="JSON_Object" href="#dfn-json_object">JSON Object</a>s that conform to the
context syntax as described in this document.</p>

<p>External JSON-LD context documents <em class="rfc2119" title="may">may</em> contain extra information located
outside of the <code>@context</code> key, such as
documentation about the <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>es declared in the document. It is
also <em class="rfc2119" title="recommended">recommended</em> that a human-readable document encoded in HTML+RDFa 
[<cite><a class="bibref" rel="biblioentry" href="#bib-HTML-RDFA">HTML-RDFA</a></cite>] or other Linked Data compatible format is served as well to
explain the correct usage of the JSON-LD context document.
</p>

</div>

<div id="vocabulary-prefixes" class="section">
  <h3><span class="secno">4.2 </span>Vocabulary Prefixes</h3>
  <p>
    Vocabulary terms in Linked Data documents may draw from a number of
    different Web vocabularies. At times, declaring every single term that
    a document uses can require the developer to declare tens, if not
    hundreds of potential vocabulary terms that may be used across an
    application. This is a concern for at least three reasons; the
    first is the cognitive load on the developer, the second is
    the serialized size of the context, the third is future-proofing
    application contexts. In order to address these issues, the concept of a
    <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a> mechanism is introduced.</p>
  <p>
    A <dfn title="prefix" id="dfn-prefix-1">prefix</dfn> is a compact way of expressing a base
    <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a> to a <a class="tref internalDFN" title="Web_Vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>.
    Generally, these prefixes are used by concatenating the <em>prefix</em> and
    a <em>term</em> separated by a colon (<code>:</code>).
    The prefix is a short string that identifies a particular Web vocabulary.
    For example, the prefix <code>foaf</code> may be used as a short
    hand for the Friend-of-a-Friend Web Vocabulary, which is identified using
    the IRI <code>http://xmlns.com/foaf/0.1/</code>. A developer may append any of
    the FOAF Vocabulary terms to the end of the prefix to specify a short-hand
    version of the full IRI for the vocabulary term. For example,
    <code>foaf:name</code> would be expanded out to the IRI
    <code>http://xmlns.com/foaf/0.1/name</code>. Instead of having to remember
    and type out the entire IRI, the developer can instead use the prefix in
    their JSON-LD markup.
  </p>
  <p>
    The ability to use <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>es reduces the need for developers
    to declare every vocabulary term that they intend to use in
    the JSON-LD context. This reduces document serialization size because
    every vocabulary term need not be declared in the context.
    <a class="tref internalDFN" title="Prefix" href="#dfn-prefix-1">Prefix</a> also
    reduce the cognitive load on the developer. It is far easier to
    remember <code>foaf:name</code> than it is to remember
    <code>http://xmlns.com/foaf/0.1/name</code>. The use of prefixes also
    ensures that a context document does not have to be updated in lock-step
    with an externally defined <a class="tref internalDFN" title="Web_Vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>. Without prefixes, a developer
    would need to keep their application context terms in lock-step with an
    externally defined Web Vocabulary. Rather, by just declaring the
    Web Vocabulary prefix, one can use new terms as they're declared
    without having to update the application's JSON-LD context.
  </p>
  <p>Consider the following example:</p>
  <pre class="example">{
  &quot;@context&quot;: {
    <span class="diff">&quot;dc&quot;: &quot;http://purl.org/dc/elements/1.1/&quot;,</span>
    <span class="diff">&quot;ex&quot;: &quot;http://example.org/vocab#&quot;</span>
  },
  &quot;@subject&quot;: &quot;http://example.org/library&quot;,
  &quot;@type&quot;: <span class="diff">&quot;ex:Library&quot;</span>,
  <span class="diff">&quot;ex:contains&quot;</span>: {
    &quot;@subject&quot;: &quot;http://example.org/library/the-republic&quot;,
    &quot;@type&quot;: <span class="diff">&quot;ex:Book&quot;</span>,
    <span class="diff">&quot;dc:creator&quot;</span>: &quot;Plato&quot;,
    <span class="diff">&quot;dc:title&quot;</span>: &quot;The Republic&quot;,
    <span class="diff">&quot;ex:contains&quot;</span>: {
      &quot;@subject&quot;: &quot;http://example.org/library/the-republic#introduction&quot;,
      &quot;@type&quot;: <span class="diff">&quot;ex:Chapter&quot;</span>,
      <span class="diff">&quot;dc:description&quot;</span>: &quot;An introductory chapter on The Republic.&quot;,
      <span class="diff">&quot;dc:title&quot;</span>: &quot;The Introduction&quot;
    },
  },
}</pre>
  <p>
    In this example, two different vocabularies are referred to using
    prefixes. Those prefixes are then used as type and property values using
    the <code>prefix:term</code> notation.
  </p>
  <p>
    Prefixes, also known as CURIEs, are defined more formally in RDFa Core 1.1,
    <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6
    &quot;CURIE Syntax Definition&quot;</a></cite> [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>].
    JSON-LD does not support the square-bracketed CURIE syntax as the
    mechanism is not required to disambiguate IRIs in a JSON-LD document like
    it is in HTML documents.
  </p>
</div>

<div id="automatic-typing" class="section">
<h3><span class="secno">4.3 </span>Automatic Typing</h3>

<p>Since JSON is capable of expressing typed information such as doubles,
integers, and boolean values. As demonstrated below, JSON-LD utilizes that
information to create <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s:</p>

<pre class="example">{
...
  // The following two values are automatically converted to a type of xsd:double
  // and both values are equivalent to each other.
  &quot;measure:cups&quot;: <span class="diff">5.3</span>,
  &quot;measure:cups&quot;: <span class="diff">5.3e0</span>,
  // The following value is automatically converted to a type of xsd:double as well
  &quot;space:astronomicUnits&quot;: <span class="diff">6.5e73</span>,
  // The following value should never be converted to a language-native type
  &quot;measure:stones&quot;: <span class="diff">{ &quot;@literal&quot;: &quot;4.8&quot;, &quot;@datatype&quot;: &quot;xsd:decimal&quot; }</span>,
  // This value is automatically converted to having a type of xsd:integer
  &quot;chem:protons&quot;: <span class="diff">12</span>,
  // This value is automatically converted to having a type of xsd:boolean
  &quot;sensor:active&quot;: <span class="diff">true</span>,
...
}</pre>

<p class="note">When dealing with a number of modern programming languages,
including JavaScript ECMA-262, there is no distinction between
<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is,
the <a class="tref internalDFN" title="number" href="#dfn-number">number</a> <code>5.3</code> and the <a class="tref internalDFN" title="number" href="#dfn-number">number</a>
<code>5.3e0</code> are treated as if they were the same. When converting from
JSON-LD to a language-native format and back, datatype information is lost in a
number of these languages. Thus, one could say that <code>5.3</code> is a
<strong>xsd:decimal</strong> and <code>5.3e0</code> is an
<strong>xsd:double</strong> in JSON-LD, but when both values are
converted to a language-native format the datatype difference between the two
is lost because the machine-level representation will almost always be a
<strong>double</strong>.
Implementers should be aware of this potential round-tripping issue between
<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
objects with a datatype of <strong>xsd:decimal</strong> <em class="rfc2119" title="must not">must not</em> be converted
to a language native type.
</p>

</div>

<div id="type-coercion" class="section">
<h3><span class="secno">4.4 </span>Type Coercion</h3>

<p>JSON-LD supports the coercion of values to particular data types.
Type coercion allows someone deploying JSON-LD to coerce the incoming or
outgoing types to the proper data type based on a mapping of data type IRIs to
property types. Using type coercion, one may convert simple JSON data to
properly typed RDF data.</p>

<p>The example below demonstrates how a JSON-LD author can coerce values to
<a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s, <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s and IRIs.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
     &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
     &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
     &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
     &quot;age&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;,
     &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
<span class="diff">     &quot;@coerce&quot;:
     {
        &quot;xsd:integer&quot;: &quot;age&quot;,
        &quot;@iri&quot;: &quot;homepage&quot;
     }</span>
  },
  &quot;name&quot;: &quot;John Smith&quot;,
  &quot;age&quot;: <span class="diff">&quot;41&quot;</span>,
  &quot;homepage&quot;: <span class="diff">&quot;http://example.org/home/&quot;</span>
}</pre>

<p>The example above would generate the following triples:</p>

<pre class="example">_:bnode1
   &lt;http://xmlns.com/foaf/0.1/name&gt;
      &quot;John Smith&quot; .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      &quot;41&quot;^^http://www.w3.org/2001/XMLSchema#integer .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/homepage&gt;
      &lt;http://example.org/home/&gt; .</pre>

</div>

<div id="chaining" class="section">
  <h3><span class="secno">4.5 </span>Chaining</h3>
  <p>
    Object <dfn title="chaining" id="dfn-chaining">chaining</dfn> is a JSON-LD feature that allows an author to
    use the definition of JSON-LD objects as <a class="tref internalDFN" title="property" href="#dfn-property">property</a> values. This
    is a commonly used mechanism for creating a parent-child relationship
    between two <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s.
  </p>
  <p>The example shows an two subjects related by a property from the first
  subject:</p>

  <pre class="example">{
...
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">knows</span>&quot;: {
    &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">Person</span>&quot;,
    &quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">Gregg Kellogg</span>&quot;,
  }
...
}</pre>

  <p>
    An object definition, like the one used above, <em class="rfc2119" title="may">may</em> be used as a
    JSON value at any point in JSON-LD.
  </p>
</div>

<div id="identifying-unlabeled-nodes" class="section">
<h3><span class="secno">4.6 </span>Identifying Unlabeled Nodes</h3>

<p>At times, it becomes necessary to be able to express information without
being able to specify the subject. Typically, this type of node is called
an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are
automatically created if a subject is not specified using the
<code>@subject</code> keyword. However, authors may provide identifiers for
unlabeled nodes by using the special <code>_</code> (underscore)
<a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>. This allows to reference the node locally within the
document but not in an external document.</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;<span class="diff">_:foo</span>&quot;,
...
}</pre>

<p>The example above would set the subject to <code>_:foo</code>, which can
then be used later on in the JSON-LD markup to refer back to the
unlabeled node. This practice, however, is usually frowned upon when
generating Linked Data. If a developer finds that they refer to the unlabeled
node more than once, they should consider naming the node using a resolve-able
IRI.
</p>

</div>

<div id="aliasing-keywords" class="section">
<h3><span class="secno">4.7 </span>Aliasing Keywords</h3>

<p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
to be aliased. This feature allows more legacy JSON content to be supported
by JSON-LD. It also allows developers to design domain-specific implementations
using only the JSON-LD context.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
     <span class="diff">&quot;url&quot;: &quot;@subject&quot;</span>,
     <span class="diff">&quot;a&quot;: &quot;@type&quot;</span>,
     &quot;name&quot;: &quot;http://schema.org/name&quot;
  },
  &quot;url&quot;: &quot;http://example.com/about#gregg&quot;,
  &quot;a&quot;: &quot;http://schema.org/Person&quot;,
  &quot;name&quot;: &quot;Gregg Kellogg&quot;
}</pre>

<p>In the example above, the <code>@subject</code> and <code>@type</code>
keywords have been given the aliases <strong>url</strong> and
<strong>a</strong>, respectively.
</p>

</div>

<div id="normalization" class="section">
<h3><span class="secno">4.8 </span>Normalization</h3>

<p>Normalization is the process of taking <a class="tref" title="JSON-LD_input">JSON-LD input</a> and
performing a deterministic transformation on that input that results in a
<a class="tref" title="JSON-LD_output">JSON-LD output</a> that any conforming JSON-LD processor would have
generated given the same input. The problem is a fairly difficult technical
problem to solve because it requires a directed graph to be ordered into a
set of nodes and edges in a deterministic way. This is easy to do when all of
the nodes have unique names, but very difficult to do when some of the nodes
are not labeled.
</p>

<p>Normalization is useful when comparing two graphs against one another,
when generating a detailed list of differences between two graphs, and
when generating a cryptographic digital signature for information contained
in a graph or when generating a hash of the information contained in a graph.
</p>

<p>The example below is an un-normalized JSON-LD document:</p>

<pre class="example">{
   &quot;@context&quot;:
   {
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
      &quot;@coerce&quot;:
      {
         &quot;@iri&quot;: [&quot;homepage&quot;]
      }
   },
   &quot;name&quot;: &quot;Manu Sporny&quot;,
   &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;
}</pre>

<p>The example below is the normalized form of the JSON-LD document above:</p>

<p class="note">Whitespace is used below to aid readability. The normalization
algorithm for JSON-LD removes all unnecessary whitespace in the fully
normalized form.</p>

<pre class="example">[{
    &quot;@subject&quot;:
    {
        &quot;@iri&quot;: &quot;_:c14n0&quot;
    },
    &quot;http://xmlns.com/foaf/0.1/homepage&quot;:
    {
        &quot;@iri&quot;: &quot;http://manu.sporny.org/&quot;
    },
    &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;
}]</pre>

<p>Notice how all of the <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s have been expanded and sorted in
alphabetical order. Also, notice how the <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> has been
labeled with a <a class="tref" title="blank_node_identifier">blank node identifier</a>. Normalization ensures that any arbitrary
graph containing exactly the same information would be normalized to exactly
the same form shown above.</p>

</div>

</div>

<div class="appendix section" id="markup-examples">

<!-- OddPage -->
<h2><span class="secno">A. </span>Markup Examples</h2>

<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
express semantic data marked up in other languages such as RDFa, Microformats,
and Microdata. These sections are merely provided as proof that JSON-LD is
very flexible in what it can express across different Linked Data approaches.
</p>

<div id="rdfa" class="section">
<h3><span class="secno">A.1 </span>RDFa</h3>

<p>The following example describes three people with their respective names and
homepages.</p>

<pre class="example">&lt;div <span class="diff">prefix=&quot;foaf: http://xmlns.com/foaf/0.1/&quot;</span>&gt;
   &lt;ul&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/bob/&quot; property=&quot;foaf:name&quot; </span>&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/eve/&quot; property=&quot;foaf:name&quot; </span>&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/manu/&quot; property=&quot;foaf:name&quot; </span>&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;</pre>

<p>An example JSON-LD implementation is described below, however, there are
other ways to mark-up this information such that the context is not
repeated.</p>

<pre class="example">{
  &quot;@context&quot;: { &quot;foaf&quot;: &quot;http://xmlns.com/foaf/0.1/&quot;},
  &quot;@subject&quot;: [
   {
     &quot;@subject&quot;: &quot;_:bnode1&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/bob/&quot;,
     &quot;foaf:name&quot;: &quot;Bob&quot;
   },
   {
     &quot;@subject&quot;: &quot;_:bnode2&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/eve/&quot;,
     &quot;foaf:name&quot;: &quot;Eve&quot;
   },
   {
     &quot;@subject&quot;: &quot;_:bnode3&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/manu/&quot;,
     &quot;foaf:name&quot;: &quot;Manu&quot;
   }
  ]
}</pre>

</div>

<div id="microformats" class="section">
<h3><span class="secno">A.2 </span>Microformats</h3>

<p>The following example uses a simple Microformats hCard example to express
how the Microformat is represented in JSON-LD.</p>

<pre class="example">&lt;div class=&quot;vcard&quot;&gt;
 &lt;a class=&quot;url fn&quot; href=&quot;http://tantek.com/&quot;&gt;Tantek Çelik&lt;/a&gt;
&lt;/div&gt;</pre>

<p>The representation of the hCard expresses the Microformat terms in the
context and uses them directly for the <code>url</code> and <code>fn</code>
properties. Also note that the Microformat to JSON-LD processor has
generated the proper URL type for <code>http://tantek.com</code>.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
    &quot;vcard&quot;: &quot;http://microformats.org/profile/hcard#vcard&quot;,
    &quot;url&quot;: &quot;http://microformats.org/profile/hcard#url&quot;,
    &quot;fn&quot;: &quot;http://microformats.org/profile/hcard#fn&quot;,
    &quot;@coerce&quot;: { &quot;@iri&quot;: &quot;url&quot; }
  },
  &quot;@subject&quot;: &quot;_:bnode1&quot;,
  &quot;@type&quot;: &quot;vcard&quot;,
  &quot;url&quot;: &quot;http://tantek.com/&quot;,
  &quot;fn&quot;: &quot;Tantek Çelik&quot;
}</pre>

</div>

<div id="microdata" class="section">
<h3><span class="secno">A.3 </span>Microdata</h3>

<p>The Microdata example below expresses book information as a Microdata Work
item.
</p>

<pre class="example">&lt;dl itemscope
    itemtype=&quot;http://purl.org/vocab/frbr/core#Work&quot;
    itemid=&quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;&gt;
 &lt;dt&gt;Title&lt;/dt&gt;
 &lt;dd&gt;&lt;cite itemprop=&quot;http://purl.org/dc/terms/title&quot;&gt;Just a Geek&lt;/cite&gt;&lt;/dd&gt;
 &lt;dt&gt;By&lt;/dt&gt;
 &lt;dd&gt;&lt;span itemprop=&quot;http://purl.org/dc/terms/creator&quot;&gt;Wil Wheaton&lt;/span&gt;&lt;/dd&gt;
 &lt;dt&gt;Format&lt;/dt&gt;
 &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
     itemscope
     itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
     itemid=&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;&gt;
  &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/BOOK&quot;&gt;
  Print
 &lt;/dd&gt;
 &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
     itemscope
     itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
     itemid=&quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;&gt;
  &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/EBOOK&quot;&gt;
  Ebook
 &lt;/dd&gt;
&lt;/dl&gt;</pre>

<p>Note that the JSON-LD representation of the Microdata information stays
true to the desires of the Microdata community to avoid contexts and
instead refer to items by their full IRI.</p>

<pre class="example">[
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Work&quot;,
    &quot;http://purl.org/dc/terms/title&quot;: &quot;Just a Geek&quot;,
    &quot;http://purl.org/dc/terms/creator&quot;: &quot;Whil Wheaton&quot;,
    &quot;http://purl.org/vocab/frbr/core#realization&quot;:
      [&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;, &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;]
  },
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
    &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/BOOK&quot;
  },
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
    &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/EBOOK&quot;
  }
]</pre>
</div>
</div>

<div class="appendix section" id="mashing-up-vocabularies">

<!-- OddPage -->
<h2><span class="secno">B. </span>Mashing Up Vocabularies</h2>

<p>Developers would also benefit by allowing other vocabularies to be used
automatically with their JSON API. There are over 200
<a class="tref internalDFN" title="Web_Vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> Documents that are available for use on the Web
today. Some of these vocabularies are:
</p>

<ul>
   <li>RDF - for describing information about objects and concepts on the Web.</li>
   <li>RDFS - for expressing things like labels and comments.</li>
   <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
   <li>Dublin Core - for describing creative works.</li>
   <li>FOAF - for describing social networks.</li>
   <li>Calendar - for specifying events.</li>
   <li>SIOC - for describing discussions on blogs and websites.</li>
   <li>CCrel - for describing Creative Commons and other types of licenses.</li>
   <li>GEO - for describing geographic location.</li>
   <li>VCard - for describing organizations and people.</li>
   <li>DOAP - for describing projects.</li>
</ul>

<p>You can use these vocabularies in combination, like so:</p>

<pre class="example">{
  &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">foaf:Person</span>&quot;,
  &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">foaf:homepage</span>&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;<span class="diff">sioc:avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Developers can also specify their own Vocabulary documents by modifying the
<a class="tref" title="active_context">active context</a> in-line using the <code>@context</code> keyword,
like so:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: { &quot;myvocab&quot;: &quot;http://example.org/myvocab#&quot; }</span>,
  &quot;@type&quot;: &quot;foaf:Person&quot;,
  &quot;foaf:name&quot;: &quot;Manu Sporny&quot;,
  &quot;foaf:homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;sioc:avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;<span class="diff">,
  &quot;myvocab:personality&quot;: &quot;friendly&quot;</span>
}</pre>

<p>The <code>@context</code> keyword is used to change how the JSON-LD
processor evaluates key-value pairs. In this case, it was used to
map one string ('myvocab') to another string, which is interpreted as
a <a class="tref internalDFN" title="IRI" href="#dfn-iri">IRI</a>. In the example above, the <code>myvocab</code> string is replaced
with &quot;<code>http://example.org/myvocab#</code>&quot; when it
is detected. In the example above, &quot;<code>myvocab:personality</code>&quot; would
expand to &quot;<code>http://example.org/myvocab#personality</code>&quot;.</p>

<p>This mechanism is a short-hand, called a <a class="tref internalDFN" title="Web_Vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> <a class="tref internalDFN" title="prefix" href="#dfn-prefix-1">prefix</a>,
and provides developers an unambiguous way to map any JSON value to RDF.</p><p>

</p></div>

<div class="appendix section" id="iana-considerations">

<!-- OddPage -->
<h2><span class="secno">C. </span>IANA Considerations</h2>

<p>This section is included merely for standards community review and will be
submitted to the Internet Engineering Steering Group if this specification
becomes a W3C Recommendation.</p>

<dl>
  <dt>Type name:</dt>
  <dd>application</dd>
  <dt>Subtype name:</dt>
  <dd>ld+json</dd>
  <dt>Required parameters:</dt>
  <dd>None</dd>
  <dt>Optional parameters:</dt>
  <dd>
    <dl>
      <dt><code>form</code></dt>
      <dd>Determines the serialization form for the JSON-LD document. Valid
        values include; <code>compacted</code>, <code>expanded</code>,
        <code>framed</code>, and <code>normalized</code>. Other values are
        allowed, but must be pre-pended with a <code>x-</code> string until
        they are clearly defined by a stable specification. If no form
        is specified in an HTTP request header to a responding application,
        such as a Web server, the application <em class="rfc2119" title="may">may</em> choose any form. If no
        form is specified for a receiving application, the form <em class="rfc2119" title="must not">must not</em>
        be assumed to take any particular form.</dd>
      <div class="issue">It is currently <a href="https://github.com/json-ld/json-ld.org/issues/14"> being discussed to remove form=framed</a> from this specification as there are several issues with it.</div>
    </dl>
  </dd>
  <dt>Encoding considerations:</dt>
  <dd>The same as the <code>application/json</code> MIME media type.</dd>
  <dt>Security considerations:</dt>
  <dd>Since JSON-LD is intended to be a pure data exchange format for
    directed graphs, the serialization <em class="rfc2119" title="should not">should not</em> be passed through a
    code execution mechanism such as JavaScript's <code>eval()</code>
    function. It is <em class="rfc2119" title="recommended">recommended</em> that a conforming parser does not attempt to
    directly evaluate the JSON-LD serialization and instead purely parse the
    input into a language-native data structure. </dd>
  <dt>Interoperability considerations:</dt>
  <dd>Not Applicable</dd>
  <dt>Published specification:</dt>
  <dd>The <a href="http://json-ld/spec/latest/">JSON-LD</a> specification.</dd>
  <dt>Applications that use this media type:</dt>
  <dd>Any programming environment that requires the exchange of
    directed graphs. Implementations of JSON-LD have been created for
    JavaScript, Python, Ruby, PHP and C++.
  </dd>
  <dt>Additional information:</dt>
  <dd>
    <dl>
      <dt>Magic number(s):</dt>
      <dd>Not Applicable</dd>
      <dt>File extension(s):</dt>
      <dd>.jsonld</dd>
      <dt>Macintosh file type code(s):</dt>
      <dd>TEXT</dd>
    </dl>
  </dd>
  <dt>Person &amp; email address to contact for further information:</dt>
  <dd>Manu Sporny &lt;msporny@digitalbazaar.com&gt;</dd>
  <dt>Intended usage:</dt>
  <dd>Common</dd>
  <dt>Restrictions on usage:</dt>
  <dd>None</dd>
  <dt>Author(s):</dt>
  <dd>Manu Sporny, Gregg Kellogg, Dave Longley</dd>
  <dt>Change controller:</dt>
  <dd>W3C</dd>
</dl>

</div>

<div class="appendix section" id="acknowledgements">

<!-- OddPage -->
<h2><span class="secno">D. </span>Acknowledgements</h2>

<p>The editors would like to thank Mark Birbeck, who provided a great deal of
the initial push behind the JSON-LD work via his work on RDFj,
Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and
performed several implementations of the specification, and Ian Davis, who
created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard
Cyganiak for their input on the specification. Another huge thank you goes out
to Dave Longley who designed many of the algorithms used in this specification,
including the normalization algorithm which was a monumentally difficult
design challenge.
</p>
</div>



<div id="references" class="appendix section">
<!-- OddPage -->
<h2><span class="secno">E. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">E.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-BCP47">[BCP47]</dt><dd>A. Phillips, M. Davis. <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>
</dd><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a> 
</dd><dt id="bib-RFC3987">[RFC3987]</dt><dd>M. Dürst; M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRIs).</cite></a> January 2005. Internet RFC 3987. URL: <a href="http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a> 
</dd><dt id="bib-RFC4627">[RFC4627]</dt><dd>D. Crockford. <a href="http://www.ietf.org/rfc/rfc4627.txt"><cite>The application/json Media Type for JavaScript Object Notation (JSON)</cite></a> July 2006. Internet RFC 4627. URL: <a href="http://www.ietf.org/rfc/rfc4627.txt">http://www.ietf.org/rfc/rfc4627.txt</a>
</dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a> 
</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">E.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-ECMA-262">[ECMA-262]</dt><dd><a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"><cite>ECMAScript Language Specification, Third Edition.</cite></a> December 1999. URL: <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a> 
</dd><dt id="bib-HTML-RDFA">[HTML-RDFA]</dt><dd>Manu Sporny; et al. <a href="http://www.w3.org/TR/rdfa-in-html/"><cite>HTML+RDFa</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/rdfa-in-html/">http://www.w3.org/TR/rdfa-in-html/</a> 
</dd><dt id="bib-MICRODATA">[MICRODATA]</dt><dd>Ian Hickson; et al. <a href="http://www.w3.org/TR/microdata/"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/microdata/">http://www.w3.org/TR/microdata/</a> 
</dd><dt id="bib-MICROFORMATS">[MICROFORMATS]</dt><dd><a href="http://microformats.org"><cite>Microformats</cite></a>. URL: <a href="http://microformats.org">http://microformats.org</a> 
</dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd>Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
</dd></dl></div></div></body></html>
